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  #1  
Old 10-05-2014, 02:54 PM
n10 n10 is offline
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w108 vacuum advance hose

Can someone with an m130 dual carb engine help me out for moment?

On the front carb I am seeing 2 vac line plugs that point toward the front of the car. Does the one closer to the top of the carb go back to the dizzy? If so, where does the lower line goto? The lower line looks like its going to the exhaust manifold....

Is there a vacuum line diagram out there?


Thanks!
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1969 w108 280s

Last edited by n10; 10-05-2014 at 04:59 PM.
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  #2  
Old 10-06-2014, 11:59 AM
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I have the 68, so there's only one vacuum nipple on the carb. AFAIK, the vacuum advance should be on a ported nipple - sees no vacuum on closed throttle and full vacuum with any amount of opening.

If one of your vacuum nipple is ported, it's likely the one you need.
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Old 10-07-2014, 10:41 AM
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Not sure if you've seen this, but the bottom post on this page has FSM scans on the Zenith:

Online Resources - Page 3 - Mercedes-Benz Forum
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Old 10-07-2014, 11:58 AM
n10 n10 is offline
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I have not see that! Awesome stuff there

Thanks Mosu.

I have a different diaphram on my diz that has a nipple on the front and the back, (that sounded weird).
I ran the advance line to upper inlet on the carb and it seems to like that better. The lower inlet has quite abit of vac to it so for kicks I just plugged it. Everything seems to be fine.
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Old 10-07-2014, 12:59 PM
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No problem! Glad you have something that works. The upper inlet is probably ported.

You might have both vac advance and retard - retard at idle for emission purposes and advance for off-idle conditions. Of course, I'm speculating wildly now and hope a more experienced member can chime in to set the record straight.
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Old 06-05-2018, 10:11 PM
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Vacuum lines on distributor?

Trouble with my W108 1970 280S. Zenith secondaries are not getting fuel (INAT 35/40). Trying to determine if I have a vacuum leak. There are 2 lines running to the distributor vacuum diaphragm (one to either side). The one on the front side appears to operate the advance mechanism. What function does the second vac line (red in pic) serve? Car has 34K original miles.
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  #7  
Old 06-06-2018, 07:40 AM
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one is advance and one is retard.

The lines should be connected to little mushroom-like cans that are electrically controlled valves. From there the lines either run to fresh air or a vacuum source.

-CTH
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Old 06-06-2018, 11:29 AM
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Thanks
Do you know which line is which? Trying to determine if a vacuum leak is causing my secondaries to not get fuel.
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Old 06-06-2018, 02:49 PM
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Secondary barrels have vacuum cells on them which often crack. Once that happens you won't get any fuel out them.
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Old 06-06-2018, 02:56 PM
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We should note that the question of fuel flow at the carburetors, and the question of the function/connection of vacuum lines at the distributor are separate, unrelated subjects.
Separate threads would be in order.
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  #11  
Old 06-06-2018, 06:29 PM
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Not really. Vacuum ports run to different controls but they're all still vacuum operated. Ignition could be a different thread but not where it relates to this one and where vacuum is concerned.
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Old 06-06-2018, 07:27 PM
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BD:

Greater familiarity with the operation of the Second Stage of the INAT carburetor would be helpful. The vacuum signal that is supplied to the diaphragm of the Second Stage is entirely internal, originates at the top of the venturies of both stages, and is not connected to any ports that supply a vacuum signal to any external consumer. The operation of the Second Stage, including its fuel flow, is independent of any external vacuum connected devices. The subjects are indeed separate.
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Old 06-06-2018, 10:32 PM
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Do the vacuum lines not share a connection at the electrical valve (mushroom shaped) connections. Would an issue with this valve affect carbs and advance?
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Old 06-06-2018, 10:47 PM
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Quote:
Originally Posted by Atchisvw View Post
Do the vacuum lines not share a connection at the electrical valve (mushroom shaped) connections. Would an issue with this valve affect carbs and advance?

A fault in the external vacuum lines and/or valves can affect the vacuum advance operation, but will not affect the operation of the Second Stages of the carburetors. Please see prior post.
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Old 06-07-2018, 12:06 AM
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Quote:
Originally Posted by Frank Reiner View Post
BD:

Greater familiarity with the operation of the Second Stage of the INAT carburetor would be helpful. The vacuum signal that is supplied to the diaphragm of the Second Stage is entirely internal, originates at the top of the venturies of both stages, and is not connected to any ports that supply a vacuum signal to any external consumer. The operation of the Second Stage, including its fuel flow, is independent of any external vacuum connected devices. The subjects are indeed separate.
You are right about how the secondary system works. I've had them apart many times and I'm familiar enough with them but I don't work on that stuff every day so it's easy to forget.
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